Telescope.



PATENTED MAY 12, 1903.

G. FORBES. I TELESCOPE. APPLICATION rum) PEI-B. s, 1903.

10 MODEL.

' Fig. 2

Patented may 12, 1903.

PATENT OFFICE- GEORGE FORBES, OF WESTMINSTER, ENGLAND.

TELESCOPE.

SPECIFICATION ,formingpart Of LGtfilS Patent N0. 727,776, dated my 12, 1903.

Application filedfebruary 6,1908. Serial No. 142,202. (No model.)

To all whom it concern:

Beitknown that I, GnoRcnFonBEs, Fellow of the Royal Society, a subject of the King of. Great Britain, residing at 3 4 Great George street, in the city of Westminster, England, hsveinventedcertain new and useful in? movements in Telescopes, of which the following is a specification.

This invention relates to telescopes of the class in which an erect image is obtained by internal reflections in s prism instead of by an erecting eyepiece; and its object is to obtain this end Without the loss of light and also to provide :i-ready adjustment for the varying distance between the eyes of different observers without changing the distance between the objectives. When two telescopes are combined to form a binocular, the distance between the eyes is varied by means of rlromboidal prism of glass, which by two int nsl reflections sends the ray into the not along the axis of the telescope, but psreli te'it. Thus by rotating one or both eyepie .shout the optic axis the distance between the rays is changed.

Figure 1 is e sections-l side elevation, and is e front elevation, of a binocular telescope made according to this invention" Fig, 3 is a front elevation, to a larger scale, of one of the prisms c. Fig. l is n plan. Fig. is a side elevation, and Figs'o are each a section on the lines 6 6, Figs. 3 ends, but iookingin opposite directions. Fig, 7 is section on the line 7 7, 5 end 6. '7" is a perspective viewof one of the n .5115. Fig. Sis isicie elevation, s isrger sonic, of one of the irisins f.

M ais the casing, and 71 are the objectives find in the casing, their distance apart being i erei ore constant.

tie the prism. {Shown separately at Figs. 3

piece.

to 6.) It has four operative faces 1, 2, 3, and 4:, the ray from the objective entering the prism at the face 1 being totally reflected internally at the faces 2 and 3 and emerging at the face 4, from whence it passes to the eye- The faces 1 end 4 are at right angles to each other, as shown at Figs. 5 and 6, and so, also, are the faces 2 and 3, as shown at Fig. 7,. lhe line of intersection d e of the faces 2 and 3 makes an angle of forty-five degrees with the faces 1 and. 4, as shown at Figs, 6. The effect of the prism c is to reversethe image, so that a correct image is oba tained without the use of an erecting eye-- piece, and since the reflections 'at the faces 2 and 3v are total internal reflections there is practically no loss of light.

fis arhomboidal prism in the ordinary 8.5--

tnonomicel eyepiece 9. As shown at. Fig. 8, the .e'ff ct of the prismf is to deflect the ray sidewis ie, so that it no longer passes along the axis of the telescope, but parallelto it, so that by rotatingone or both of the eyepieces about the optic axis the distance between the rays is changed.

- What I claim is' 1. The combination of an objective, an eyepiece a prism having four operative faces, namely a pair of transmitting-faces anb a pair of reflecting-faces, the faces of each pcir being at ri "it toggles to each other and the line of into Jinn oi the feces of one pair making on a of forty-live degrees with the faces of T or pair;

2. The combination with a, telescopic eyepiece of s rhomboidel prism free to rotate about the optic axis.

GEORGE FORBES.

Witnesses:

FBEDK. WEATHERLY. illness Broncos. 

